Nickel(II) Complexes of N‐Alkyl‐Substituted Diamino Diamides in Aqueous Solution

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Equilibrium constants are deter mined for the protonation and metal complexation of the nickel(II) complexes with 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N,N′‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐ diazaundecane diamide (4‐Me‐L‐2,3,2), in 0.10 M KCl at 25.0°C. The formation kinetics of these nickel (II) complexes have been studied under the same conditions with use of the stopped‐flow technique. The possible path ways for the complexation reaction of nickel (II) with these ligands are discussed. The first metal‐nitrogen bond formation is proposed as the rate‐determining step for the reactions of nickel (II) with the unprotonated ligands; proton loss is the rate‐limiting step in the reactions of nickel (II) with the monoprotonated ligands. Similarly, in dissociation reactions of these nickel (II) complexes, the rate‐determining step for the water dissociation pathway is the break age of the second nickel‐nitrogen bond; the rate‐determining step for the proton‐assisted path way is the protonation of the released amino group. The important factors determining the reactivity of these complexes are considered. The kinetic results of the formation and dissociation reactions of these complexes are consistent with dissociative mechanism.

Complexation Kinetics of N‐Alkyl‐Substituted Diamino Diamides with Nickel (II) in Aqueous Solution

Chao¹,

Huang²

2001

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Kinetics of Acid‐Catalyzed Dissociation of Nickel (II) N‐Alkyl‐Substituted Diamino Diamide Complexes

Chao

2002

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The dis so ci a tion ki net ics of the nickel (II) com plexes of 4-methyl-4,7-diazadecanediamide (4-Me-L-2,2,2), 4,7-dimethyl-4,7-diazadecanediamide (4,7-N,N′-Me2-L-2,2,2), 4-ethyl-4,7-diazadecanediamide (4-Et-L-2,2,2), and 4-methyl-4,8-diazaundecanediamide (4-Me-L-2,3,2) have been stud ied at 25.0 °C and µ = 4.0 M (NaClO4 + HClO4) by the stopped-flow method. These re ac tions are spe cific-acid cat a lyzed; how ever, the rate con stants of these re ac tions do not de pend on the con cen tra tions of ace tic, chloro acetic, and dichloroacetic ac ids. At pH val ues be low 1.0, both the pro ton-assisted and the di rect protonation path ways make contri bu tions to the rates. The ra tios of the rate con stant of dis so ci a tion by the di rect protonation path way to the rate con stant by the pro ton-assisted path way for the com plexes in aque ous so lu tion were mea sured and discussed.

Kinetics of Acid‐Catalyzed Dissociation of Copper(II) N‐Alkyl‐Substituted Diamino Diamide Complexes

Chao

Huang

2003

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The dissociation kinetics of the copper(II) complexes of 4‐methyl‐4,7‐diazadecanediamide (4‐Me‐L‐2,2,2), 4,7‐dimethyl‐4,7‐diazadecanediamide (4,7‐N,N′‐Me2‐L‐2,2,2), 4‐ethyl‐4,7‐diazadecanediamide (4‐Et‐L‐2,2,2), and 4‐methyl‐4,8‐diazaundecanediamide (4‐Me‐L‐2,3,2) have been studied at 25.0 °C and μ = 4.0 M (NaClO4 + HClO4) by the stopped‐flow method. These reactions are specific‐acid catalyzed; however, the rate constants of these reactions do not depend on the concentrations of acetic, chloroacetic, and dichloroacetic acids. At pH values below 1.4, both the proton‐assisted and the direct protonation pathways make contributions to the rates. The ratios of the rate constant of dissociation by the direct protonation pathway to the rate constant by the proton‐assisted pathway for the complexes in aqueous solution were measured and discussed.